Score the eggplants all over with a fork. Preheat a gas grill on high and grill the eggplant whole until the skins are black and blistered, about 40 minutes. Remove the skins and spoon out the insides as soon as you can handle the eggplant. Puree the pulp in a food processor, then drain the bitter liquid from the eggplant by letting it sit in a strainer over a bowl for an hour. In a small bowl, mix the lemon juice and tahini. Pound the garlic and salt together in a mortar until it is a paste, then stir into the tahini. Stir into the eggplant puree. Taste and add water to thin. Pour onto a serving platter and drizzle with olive oil, then top with parsley. Scoop with pita or Arabic flatbread.